In vehicles having internal combustion engines, it can be beneficial to discontinue fuel injection to all or some of the engine cylinders during certain operating conditions, such as during vehicle deceleration or braking. The greater the number of cylinder deactivated, or the longer cylinders are deactivated, the greater the fuel economy that can be achieved. It is known to consider a variety of factors for enabling cylinder deactivation, including: whether engine speed error is greater than a threshold value; the gear ratio of the transmission; whether vehicle speed is greater than a threshold value, whether engine load is greater than a threshold value, and whether the throttle is closed greater than a threshold value, as described in FIGS. 3A-3B below.
The inventors herein, however, have recognized a disadvantage that can be encountered when deactivating fuel injection to engine cylinders. Specifically, engine stalls can occur when trying to re-enable deactivated cylinders depending on engine speed. Further, it takes a certain duration (e.g., amount of time, or number of engine cycles) to re-enable engine firing. Thus, the inventors herein have recognized that if the cylinder deactivation condition is allowed to exist in certain conditions, then during reactivation of the cylinders it is possible that an engine stall can occur. This results in under-utilization of cylinder disablement (fuel cut-out operation) and therefore unrealized fuel economy gains.